linux-kernel - Re: [PATCH] sched/topology: One function call less in build_group_from_child_sched

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Message-Id: <20190706172223.GA12680@linux.vnet.ibm.com>
Date:   Sat, 6 Jul 2019 22:52:23 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Markus Elfring <Markus.Elfring@....de>
Cc:     kernel-janitors@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/topology: One function call less in
 build_group_from_child_sched_domain()

* Markus Elfring <Markus.Elfring@....de> [2019-07-06 16:05:17]:

> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Sat, 6 Jul 2019 16:00:13 +0200
> 
> Avoid an extra function call by using a ternary operator instead of
> a conditional statement.
> 
> This issue was detected by using the Coccinelle software.
> 
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  kernel/sched/topology.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index f751ce0b783e..6190eb52c30a 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -886,11 +886,7 @@ build_group_from_child_sched_domain(struct sched_domain *sd, int cpu)
>  		return NULL;
> 
>  	sg_span = sched_group_span(sg);
> -	if (sd->child)
> -		cpumask_copy(sg_span, sched_domain_span(sd->child));
> -	else
> -		cpumask_copy(sg_span, sched_domain_span(sd));
> -
> +	cpumask_copy(sg_span, sched_domain_span(sd->child ? sd->child : sd));

At runtime, Are we avoiding a function call?
However I think we are avoiding a branch instead of a conditional, which may
be beneficial.

>  	atomic_inc(&sg->ref);
>  	return sg;
>  }
> --
> 2.22.0
> 

-- 
Thanks and Regards
Srikar Dronamraju